This invention relates to adducts obtained from particular polyamide polymers and particular diacid molecules. It is known to produce crystalline salts from certain alkyl benzimidazole polymers, with formic acid or trifluoroacetic acid (Aharoni et al., Journal of Applied Polymer Science, vol. 21, of 1977, pages 181-189). The molecular packing modes and hydrogen bonding properties of certain complexes between monomeric amides and dicarboxylic acids have been studied (Acta Cryst., vol. B33 of 1977, pages 2719-33).